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87 votes

How many times do you have to circle the Earth to break orbit?

This depends on how much thrust you have available. With enough thrust, you don't need to be in Earth orbit at all: you can launch straight into an escape trajectory. New Horizons did this, more or ...
Hobbes's user avatar
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78 votes
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Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?

It depends on the altitude. Here is a chart from ESA and UNOOSA. Basically, anything under 500 km will fall relatively quickly, maybe 25 years. Everything under 800 km should fall within a century or ...
PearsonArtPhoto's user avatar
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71 votes

Where does space begin on planets without atmospheres?

Yet surely nobody would classify Neil Armstrong's lunar bunny-hops as suborbital spaceflights. Why not? There's no essential difference between a high-eccentricity trajectory with an apolune of 1 ...
Russell Borogove's user avatar
67 votes
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Why can't you travel to Mars in a straight line?

Only answering your first question here, and in qualitative terms: You can't travel to Mars in a straight line for the same reasons you can't throw a ball in a straight line: gravity. If you wanted to ...
Anton Hengst's user avatar
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66 votes
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What is the farthest artificial satellite in orbit in our solar system?

The term for orbits in our solar system around the Sun is Heliocentric. Closed Heliocentric Orbit The solar observation probe Ulysses is the furthest artificial satellite around the sun. It's in a ...
Jack's user avatar
  • 9,976
64 votes

Why aren't the 'bedrooms' aboard the ISS also the escape pods?

Primarily, because without a lot of extra equipment, they could at best be space coffins for the astronauts. First, they share life support with the rest of the station. Air circulated through them ...
SF.'s user avatar
  • 55k
60 votes

Why are all space initiatives designed to get to space overnight when in Nature all extreme feats are achieved in a gradual process

Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would ...
Magma's user avatar
  • 381
51 votes

Why are all trajectories in space a conic sections?

Not all trajectories in space are conic sections, only those that are a two body problem. One planet in orbit around a star is a two body problem. Only two body problems are solved by a conic section. ...
Uwe's user avatar
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47 votes
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Do you need 0 km/s velocity to crash into the sun?

Wouldn't i inevitably spiral to sun surface even if i was faster than 0km/s ? No. On reasonable timescales, an orbit will have a fixed distance of closest approach, called "periapsis." (These ...
Erin Anne's user avatar
  • 10.8k
46 votes

How many times do you have to circle the Earth to break orbit?

Zero See at: https://en.wikipedia.org/wiki/Escape_velocity for theory. Once you build enough velocity to surpass gravitational attraction, you will leave planetary orbit. A spacecraft simply ...
ingconti's user avatar
  • 499
45 votes

Escaping moons conflict with what I understand of gravity

A very good question! The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 ...
Martin Kochanski's user avatar
45 votes
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Are all satellites of all planets in the same plane?

Most large regular satellites orbit in the equatorial plane of their planet. Every planet spins, and thus has an equatorial bulge caused by centrifugal forces that over time aligns the satellites' ...
HigherIdeals's user avatar
42 votes
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Why use a retrograde orbit?

Retrograde orbits have multiple use-cases. First of all you should note that "retrograde" doesn't mean 180° inclination - everything > 90° is considered retrograde. This places all sun-synchronous ...
Polygnome's user avatar
  • 6,926
41 votes

If the Earth spun clockwise, how would that affect Space Exploration?

Primarily, locations of spaceports would change. California, not Florida would host the NASA's main launch site. Russia would be in slightly better position, able to send rockets over the Black Sea, ...
SF.'s user avatar
  • 55k
37 votes

Do simulator games use a realistic trajectory to get into orbit?

I understand the reasons behind each of this manouveurs, however I'm wondering if this is how real rockets get into orbit. Cutting off the engine and letting the rocket loose vertical speed looks ...
Russell Borogove's user avatar
36 votes
Accepted

How does a Spacecraft change its orbit?

To answer your title question: By using its engines. However you seems to be quite puzzled by the fact that velocity of an object can decrease and increase over the course of an orbit. If the orbit ...
Antzi's user avatar
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35 votes

Where does space begin on planets without atmospheres?

Ultimately, "the edge of space" is an agreed upon convention. In other words it is essentially arbitrary, something which only humans even care about (well maybe space aliens too <grin>). Yes, ...
codeslinger's user avatar
35 votes
Accepted

Do simulator games use a realistic trajectory to get into orbit?

Physics In regards to the physics, KSP is fairly realistic, other than it not modeling n-body physics (which isn't really relevant in scope of orbiting Earth/Kerbin). In regards to the engineering, ...
Flater's user avatar
  • 466
33 votes
Accepted

How is the altitude of a satellite defined, given that the Earth is not spherical?

update: 6378.137 km is what I use now. By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is ...
uhoh's user avatar
  • 149k
33 votes
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How did the USSR track Gagarin's Vostok-1 orbital flight? Was tracking capability an issue in the choice of orbit?

The Answer is on a page by Sven Grahn. No ocean going tracking ships were used. Only ground stations on the territory of the USSR. In the other answers some russian sources about the use of tracking ...
Uwe's user avatar
  • 48.9k
33 votes
Accepted

What causes a satellite's orbit to decay?

If satellites are truly far beyond the atmosphere, their orbits do not decay, except for very small perturbation effects like solar radiation pressure from the Sun or tidal forces from the Moon. But ...
SE - stop firing the good guys's user avatar
32 votes

Why did the X-15 not achieve orbit?

You're confusing units. The maximum speed of the X-15 was 7274 km/h, or about 2 km/s. Orbital speed is around 8 km/s. The X-15 didn't carry enough fuel to reach orbital speed.
Hobbes's user avatar
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32 votes
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Why is 51.8° inclination standard for Soyuz?

As Baikonur is at 45.965° north latitude, it would make sense if 45.965° was the standard inclination for Soyuz (and for the ISS). That would be a launch due east, thereby taking the greatest ...
David Hammen's user avatar
  • 73.8k
31 votes

What are the biggest challenges for high altitude rail-gun launch systems?

What you're describing is (more or less) the StarTram "gen 1" design. The reference design has: 40 tonne unmanned cargo projectile, 25 tonnes of payload, ~2 m wide, ~13 m long. A 130 km maglev ...
Starfish Prime's user avatar
30 votes
Accepted

This orbit looks wrong near a Lagrange point. Is it?

Is the orbit shown in the graphic wrong, or is my understanding of orbital mechanics lacking, having only been influenced by KSP? It's not an either-or question. The graphic is "wrong" from the ...
David Hammen's user avatar
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30 votes
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Teleporting an object into geosynchronous orbit

I'm afraid you are incorrect. An object on the equator of Earth has a velocity of ~460 m/s. A satellite in geosynchronous orbit has a velocity of ~3000 m/s. You may be confused by the fact that both ...
Organic Marble's user avatar
30 votes
Accepted

How far have astronauts been in space?

Twelve Apollo astronauts landed on and walked on the Moon Twelve more Apollo astronauts orbited the Moon without landing So that's twenty-four individuals that count towards "(except for the ...
uhoh's user avatar
  • 149k
28 votes
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The Loose Astronaut

This is a great question. I wanted to provide an answer which cited some specific, real-world situations. Currently the only people in space are those aboard the International Space Station. If anyone ...
zephyr's user avatar
  • 396
28 votes

How does a planet's gravity push away smaller bodies that would otherwise intersect its orbit?

I feel the need to correct some issues that were brought up in the other answers. Yes, gravity is an attraction-only force. But due to its relative weakness, objects in space can attain large ...
AtmosphericPrisonEscape's user avatar
28 votes

Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?

Space debris poses a real risk for spacecraft in LEO. From the Technical Report on Space Debris UN Committee on the Peaceful uses of Outer Space (Table 5), a satellite in orbit can expect to collide ...
Woody's user avatar
  • 21.4k

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